It seemed too good an opportunity to miss. Why not reach out to disaffected Liberal Democrats ahead of today's Oldham East and Saddleworth byelection by announcing a £100m government plan to re-use empty homes?

So last weekend the Lib Dem housing minister, Andrew Stunell, travelled to the constituency to hail the scheme. He was even pictured with a grateful resident.

As I blogged on Monday night, Labour was convinced that the Stunell visit breached Whitehall "purdah" rules which place restrictions on government announcements during elections and byelections. John Trickett, the shadow cabinet office minister, wrote to the cabinet secretary Sir Gus O'Donnell requesting an investigation.

O'Donnell has conducted a speedy enquiry and concluded that Stunell, one of four Lib Dems who negotiated the coalition agreement in May, had been unwise. He announced that Stunell has apologised.

This is O'Donnell's response to Trickett which appears on Labour Uncut:

January 12, 19.34

From: Gus O'DonnellTo: Jon Trickett MP

Mr Trickett

Thank you for your email sent on Monday evening about an announcement during a by-election campaign on new Government incentives to bring empty homes back into use.

I have looked urgently into the issues you raise.

The sequence of events as I have been able to establish is as follows:

Communities and Local Government (CLG) issued a press release on Friday 7 January announcing additional Government funding to bring empty homes back into use. The press release was embargoed until Monday 10 January. This was a national announcement which made no reference to Oldham and therefore would not be in breach of by-election restrictions.

Andrew Stunell visited Oldham on Saturday 8 January. As part of this he visited an empty property in Oldham that had been brought back into use by the Council. I understand that he did not refer to the planned funding announcement during his visit.

The Liberal Democrat Party issued a press release on Sunday 9 January, embargoed until Monday 10 January, referring to the Minister's visit and highlighting new government incentives to bring empty homes back into use. This was timed to coincide with the issue of the Government's press release.

Taking these events together, the Minister recognises with hindsight that his visit could have been associated in the minds of the public with a government announcement of additional funding, and has apologised for this.

The deputy prime minister and leader of the Liberal Democrats, Nick Clegg, says his party came a strong second in the Oldham East and Saddleworth byelection, which was won by Labour candidate Debbi Abrahams

Victory for Labour in Britain's first parliamentary byelection since the formation of the coalition last May as Debbie Abrahams beat the Liberal Democrat candidate Elwyn Watkins by 14,718 to 11,160 to be the next MP for Oldham East and Saddleworth